The diagnosis of a luteal phase defect (LPD) is usually straightforward and can be made within 1-2 months.

A luteal phase defect (LPD) is associated with fertility problems due to shortening of the luteal phase, the time between ovulation and the next period.

Women who monitor their basal body temperature will often note that luteal phase temperatures (temperatures between ovulation and the next menstrual period) do not stay reliably elevated for 12 days. Additionally, women who monitor the time of ovulation often notice that their next cycle begins sooner than the normal 12-16 days after ovulation. A serum progesterone test less than 14 ng/ml at about 7-10 days after ovulation may indicate LPD. Many doctors feel that an endometrial biopsy is the gold standard in diagnosing LPD. It is normally performed a few days before the next menstrual cycle is expected, ideally after a negative pregnancy test for the cycle has been obtained. If there is a discrepancy of more than two days, the lining will usually be considered out of phase.